When a patient's knee is severely damaged it may be desirous to repair and/or replace portions or the entirety of the knee with a total or partial knee replacement implant. Knee replacement surgery is a well-tolerated and highly successful procedure that can help relieve pain and restore function in injured and/or severely diseased knee joints.
In a typical knee surgery, the surgeon will expose the knee joint and laterally dislocate the patella. The anterior cruciate ligament may be excised and/or the surgeon may choose to leave the posterior cruciate ligament intact—such soft tissue removal often depends on the surgeon's preference and condition(s) of the ACL/PCL. Various surgical techniques are used to remove the arthritic joint surfaces, and the tibia and femur are typically prepared and/or resected to accept the component artificial implants. Depending upon the surgeon's preference, the component artificial implants should desirably resemble or represent the native thickness of the tibia, femur, articular cartilage, and the menisci to restore the knee to its natural alignment, movement and height.
The resection process involves the assessment of a variety of important “gaps” that the surgeon uses in planning and executing the surgical procedure, which ultimately allows the surgeon to gauge the implant's final rotation, alignment, movement and restoration of height to the joint. One “gap” existing between the tibia and the distal end of the femur is referred to as the “extension gap,” and it can include measurement or assessment of the natural gap between the bones and/or other tissues, as well as the space that is created when the bone is resected from one or more of the relevant bone surfaces. Another important “gap” that exists is between the tibia and the posterior end of the femur (when the femur is in flexion) is called the “flexion gap,” and it can include measurement or assessment of the natural gap between the bones and/or other tissues, as well as the space that is created when bone is resected from one or more of the relevant bone surfaces. Ideally, the surgeon would prefer the “gap” between the femur and the tibia to be optimized for multiple positions of the femur relative to the tibia (i.e., throughout the entirety of the joint's motion), but a common “approximation” for knee surgery is to attempt to balance the flexion gap and the extension gap of the knee, and assume that the rest of the knee motion will be acceptable during the entirety of the range of motion. Ideally, therefore, the surgeon wants both the extension gap and the flexion gap to be appropriately tensioned when the implant is placed in the joint.
In general, a surgeon does not conduct the balancing of both the flexion gap and the extension gap until some or all the bone resections have been performed. Once the desired bony resection planes have been initially created, the surgeon subsequently utilizes a variety of standard instruments to test the overall implant assembly thickness, such as blocks, spacers, and other tools to ensure proper tensioning, alignment, and rotation. Should the surgeon experience any errors in any of the variables mentioned above, the surgeon may be forced to adjust and/or recut the resection planes in either or both of the femur or tibia. This can result in longer surgery times, lead to malpositioning of implant components), improper resection cuts, malalignment of varus/valgus angle(s), and poor axial alignment that may contribute to poor artificial implant positioning, instability of the joint, and poor surgical outcomes. Using such current techniques and surgical tools may contribute to implant component failures and the need for implant revision surgery, prosthetic loosening, arthrofibrosis, deep infection and/or bone loss.